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Date:	Tue, 16 Oct 2007 15:18:03 -0700
From:	Badari <pbadari@...ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
CC:	adilger@...sterfs.com, linux-kernel@...r.kernel.org,
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH] ext2 statfs improvement for block and inode free count

Andrew Morton wrote:
> On Fri, 13 Jul 2007 18:36:54 -0700
> Badari Pulavarty <pbadari@...ibm.com> wrote:
>
>   
>> More statfs() improvements for ext2. ext2 already maintains
>> percpu counters for free blocks and inodes. Derive free
>> block count and inode count by summing up percpu counters,
>> instead of counting up all the groups in the filesystem
>> each time.
>>
>>
>> Signed-off-by: Badari Pulavarty <pbadari@...ibm.com>
>> Acked-by: Andreas Dilger <adilger@...sterfs.com>
>>
>>  fs/ext2/super.c |    4 ++--
>>  1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> Index: linux-2.6.22/fs/ext2/super.c
>> ===================================================================
>> --- linux-2.6.22.orig/fs/ext2/super.c	2007-07-13 20:06:38.000000000 -0700
>> +++ linux-2.6.22/fs/ext2/super.c	2007-07-13 20:06:51.000000000 -0700
>> @@ -1136,12 +1136,12 @@ static int ext2_statfs (struct dentry * 
>>  	buf->f_type = EXT2_SUPER_MAGIC;
>>  	buf->f_bsize = sb->s_blocksize;
>>  	buf->f_blocks = le32_to_cpu(es->s_blocks_count) - overhead;
>> -	buf->f_bfree = ext2_count_free_blocks(sb);
>> + 	buf->f_bfree = percpu_counter_sum(&sbi->s_freeblocks_counter);
>>  	buf->f_bavail = buf->f_bfree - le32_to_cpu(es->s_r_blocks_count);
>>  	if (buf->f_bfree < le32_to_cpu(es->s_r_blocks_count))
>>  		buf->f_bavail = 0;
>>  	buf->f_files = le32_to_cpu(es->s_inodes_count);
>> -	buf->f_ffree = ext2_count_free_inodes(sb);
>> + 	buf->f_ffree = percpu_counter_sum(&sbi->s_freeinodes_counter);
>>  	buf->f_namelen = EXT2_NAME_LEN;
>>  	fsid = le64_to_cpup((void *)es->s_uuid) ^
>>  	       le64_to_cpup((void *)es->s_uuid + sizeof(u64));
>>
>>     
>
> Guys, I have this patch in a stalled state pending some convincing
> demonstration/argument that it's actually a worthwhile change.
>
> How much hurt will it cause on large-numa, and how much benefit do we get
> for that hurt? 
>   
Unfortunately, I couldn't find any noticeable significant improvements 
with or without this patch.
May be none of my filesystems are large enough on a large enough NUMA 
box to verify.
Lets drop it for now and re-visit it if needed.

Thanks,
Badari

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